Furnace insulation system



Nov. 2, 1954 F. s. BLooM FURNACE INSULATION SYSTEM 4 Sheets-Sheet l Filed Aug. 14, 1950 L um mm MN INVENTOR Frede/'ick .S B/oom Nov. 2, 1954 F. s. BLooM FURNACE INSULATION SYSTEM 4 Sheets-Sheet 2 Filed Aug. 14, 1950 INVENToR Frede/"KWS B/oom Nov. 2, 1954 F. s, BLooM FURNACE INSULATION SYSTEM 4 Sheets-Sheet 3 Filed Aug. 14, 195o X Figlz INVENTOR Frede/ick S. /oom Nov. 2, 1954 F. s. BLooM FURNACE INSULATION SYSTEM Filed Aug. 14, 1950 4 Sheets-Sheet 4 l l l l l l f l l f INVENTOR Frede/'ick S. 5/0 om d? 4a l0-7144, M)

United States Patent Online y 2,693,352 y Patented Nov. 2, 1,954

mannen rNsUrsArIoN SYSTEM Frederick S. Bloom, Pittsburgh, Pa. Appiaanen August 14, 1950, serial No. 179,105 1a claims, y(ci. 26a- 6) This invention relates to means and method for insulating members mounted within high temperature furnace chambers, particularly water-cooled pipes in the supporting structure for workpieces in heat-treating furnaces such as those described in my copending application Serial No. 694,734, tiled September 4, 1946, now Patent No. 2,523,644.

A supporting structure within a furnace chamber where temperatures may be in theorder of 2000" 1:". must be compact in order to leave suicient combustion space in the chamber, must be strong enough to support heavy metal workpieces being treated in the furnace, and must be protected against injury by the high temperatures within the furnace while at the same time not seriously interfering with the efficiency and maximum temperatures of the furnace. A combination of small size with high strength dictates the use of metal in these supports, and the necessity for cooling the metal dictates the use -of hollow metal pipes through which cool water is circulated. lf water-cooled pipes with bare outer surfaces are used, however, the adsorption of heat through the metal to the cooling fluid is so great that much more fuel is wasted in heating the cooling fluid than in heating the higher temperature workpieces; for example, a furnace having bare metal supports in its lower zone requires about three times as much fuel to heat the lower zone of the furnace as the upper zone of the furnace, and no matter how much fuel is supplied to the lower zone it still remains distinctly cooler than the upper Zone. In order to correct this condition refractory insulating material is often placed around water-cooled supporting pipes, but the refractory tends to crack away after some use, principally because of the difference in thermal expansion of the inner and outer layers of the refractory material and because of the difference in the thermal expansion characteristics of the refractory material and the 'metal pipe which lit encloses. In order to overcome this difficulty various expedients have been tried. In some cases, such as shown by Schmidt Patent No. 2,436,452-, the refractory material is spaced from the metal pipe. This I have found to be disadvantageous because the air space acts as an insulator and consequently the refractory material is insufficiently cooled by the fluid within the metal pipe and the working life of the refractory material is reduced. In other cases, such as shown by Corriston Patent No. 2,022,649, the refractory material is applied directly to the water-cooled metal pipe so that it is adequately cooled by the pipe, anda large number of radially-extending metal studs are welded to the pipe to hold the refractory material inl place. This helps to retain the refractory but this system is expensive because of the large number of studs which must be welded to the pipe, and precludes any possibility of precasting the refractory before it is placed around the pipe. Moreover, the studs of Corriston extend entirely through the refractory and conduct an excessive vamount .of furnace heat to the cooling fluid in the pipe.

In accordance with my invention I overcome these difficulties and achieve a more practical and efficient insulation of a furnace support, especially in the case of a water-cooled metal supporting pipe, by securing a reticulated metal structure such as a plurality of wires around the pipe and imbedding refractory material in the wires to cover the wires and pipe andto extend solidly from the outer surface of the pipe `without any air space between the refractory and therpipe. The outer layer of the refractory loverlies jany metal which ,might conduct excessive heat to the core of the insulated structure, and at the same time the reticulated metal structure acts as a firm anchor for the refractory and prevents the refractory from falling away when it develops cracks after a period of exposure to furnace temperatures. The reticulated metal structure is readily welded or otherwise fastened to the metal pipe and can be made up of any desired number of sections. These sections may have refractory material cast thereon before being secured to a supporting pipe in a furnace chamber. This saves time and expense and is more convenient than casting the refractory in the furnace. Moreover, the time available for replacing refractory after prolonged use in a furnace is so limited that it is conventional to use wooden molds for casting the refractory in the furnace and to fire up the furnace before the refractory has hardened sufliciently to permit the molds to be removed and saved. The use of precast sections in accordance with my invention eliminates this waste of molds without loss of time and without sacrificing any of the strength and durability of the completed refractory covering. In short, one object and effect of my invention is to permit the welding of prefabricated refractory cover pieces to metal supports in furnace chambers.

I have further discovered that the reticulated metal structure can be quickly fastened to the metal supporting structure by bending a portion of the reticulated metal around a small stud welded to the pipe and entirely covered by the outer layer of insulating material, or by bending the welded stud around the reticulated metal structure. This slightly increases the time of applying the insulation initially but when sections of insulation have to be replaced it is sometimes quicker and easier to lbend small pieces of reticulated metal in the bases of the insulating sections around studs already in place on the metal support, or vice-versa, than it is to bring welding equipment into the furnace chamber in order to weld the insulating sections in place.

One' suitable form of reticulated metal structure is woven wire having a network of strands crossing over and under one another, since a portion of this structure may be injured without weakening the adjacent portions of the structure. A more expensive and stronger form of reticulated metal structure is a wire fabric comprising interlocking coils of wire extending parallel to each other and to the pipe axis. However, it is not practical to prere insulating sections having any form of woven or interlocking wire base because the wire would be exposed to high temperatures in order to prefire the inner surfaces as well as the outer surfaces of the refractory, and this would burn out the wire. I have found that this difculty'in prering can be overcome by using a plurality of separate wire strands which are not woven together and which, therefore, can be individually removed from the cast preformed insulating section while the insulating material is being prefired, and then may be replaced in the refractory before the resultant preformed section is placed on a furnace supporting pipe, where the ends of the wire strands protruding from the prered refractory are readily welded or otherwise fastened to the pipe.

Other novel features, objects and advantages of the invention will become apparent from the following description and in the accompanying drawings. i have shown in the drawings, for purposes of illustration only, certain present preferred embodiments of vmy invention,

1 in which Figure l shows a heat-treating furnace partially broken away to show the interior structure;

Figures 2, 3 and 4 show three stages of applying preformed insulating sections to a riser or crossover pipe in the lower part of the furnace shown in Figure l;

Figures 5, 6 and 7 show three succesisve stages of applying partially preformed insulating sections to a skid rail pipe in the lower part of the furnace shown in Figure l;

Figure 8 shows a partially sectioned and broken away perspective view of a pipe like that shown in Figures 2-4, with a modified form of refractory covering;

Figure 9 shows a partially broken away side view of a riser or crossover pipe with a further modied form of f rfractorycovering;

Figure is a section on line X--X in Figure 9; Figure l1 corresponds to Figure 9' but shows a different means for attaching wire in a refractory covering to an underlyingpipe;

Figurel2-is a sectionon lineXIfL-Xll in Figure ll; Figure 13 is asectional view throughfthe axis of' a riserl or crossover pipe with a still further modified form of'refractory'covering; j 1* r :Figure 14 is a section on line XIV--XIV in Figure 1.3;.and m... Figuref- 15 is a section on line XV--XVfin'Figure 13. Referring now moreyparticularly tothe drawingsdn Figure 1- there, isshownfa furnace 20 through: whicha series of metal, billets 21 arepassed on skid rails; 2 2 extending along skid rail pipes 23 and resting on holnzont'al crossovers 24-supportedon vertical risers 25. The skid- 'rail pipes,` crossovers .and risers are all in therform of` metalpipes having connected interiorpassages` for passing cooling uid such` as water therethrough in accordance with conventional practice. In -Figures 2-4 a crossover pipe 24a is shown in successive stages ofhavingrefractoryinsulation appliedk to it. InFigure 2 the lower portion of Athepipe 24a is shown covered with a preformed insulating section' 2 6 comprising a semicylindrical refractory elementx27 havingmwire fabric 2d imbedded thereinv closelfygadjacentits. innerl surface with portions of the wire protruding from the refractory materialadjacent opposite sides ofthe. pipeu24a. The section 26 is placed againstthe pipe 24g and the protruding portions 'ofthe wireare welded to the pipe atv spaced intervals 29 on both sidesofthe pipe 24a. An identical insulating-section 3,0 is placedagainst the upper portion` of the pipe 24a and is similarlyvweldedjto the pipe24a. Each of the sections 26 and 30.. extend's less than 180 aroundthe pipe 24a sO-thatlftheV protruding portions of the wire base of 'the section ,30 are spacedl from'the'corresponding" portions -of lthensection l26 andv are thereby exposed for welding tomopposite sidesof the pipe 24a as indicated' at 431n in lFigure The gap be.- tvveenv the sections 26 and, 3.0y on OppQsitersides of the pipe 24a is closed after `the Weldingoperation .by pasting plastic lrefractory material into: thesegaps, so; thatrthe pipe 24a is entirely. surrounded by a coating of refractory material asndicated in FigureV 4... :Additional sections are -added in abuttingl endto-end relationshipasrequired. Itwill be observed thatpreformed insulating sections of this tkind are suitable for use on thetyertical .risen pipes Las well as on the horizontal crossover pipes 24 shown inligurel. .I A .f .g .1 In Figures 5-*7 a horizontalrpipeZSa. supporting askid rail 32 alongits Uppersurfacedsshown inrsucessive stages o f having a refractory covering applied thereto. Inl Figure 5 there isshown a. preformed insulating'dsec-z tion 3:3v identical with the section; 26. showni'n Figure 2 and welded to the'y pipe 23a inthe same. manner as the section 26 is welded to ,the pipe ,24a in Figure- 2.,. 3In Figure 6 pieces of wire fabric 34 and35 arekshown placed around the portions 'of the pipe-23a between the opposite sides.of theskid rail 32 and. correspondingedges of the insulating section33. The Wire fabric pieces 34.and.35 are welded at intervals tothe pipe 23a and krefractory material is then pasted. against the. wire pieces 34 and 35 andis molded therearound asshown in.Fig`ure7 to form a solidlayery of refractory material imbeddedinfthe wire fabric pieces 34jand. 3,5 with `a thickness Vequal to that .of the preformed lower s ection33, so that acontinuous layer of refractorymaterialextends raround the pipe. 23a frornthe oppositev sides oftheskid rail, 32, wiitlhglt covering the top working surface of the skid ra The wire fabric 'pieces`3'4 and k35 shown in Figure 6 may take Various formsbut areillustrated in lFigure 6 as. comprising a plurality of -interlocking-coils ,of wire having helical .axes parallel to each other and to, the axis of the pipe' 23a. Thisfolrmvof ywire base is very strong, is` very effective in holding the base of thetrefrac; tory covering to the pipe; and is easy today. around a pipe with all of the coils fitting closely against the pipe, without any presetting or bending of the wire before it is applied' to the pipe.

A modified embodiment of theinvention is. shownir'l Figure 8, where a horizontal pipe 24b' (similar tothe pipe 24a in FiguresV 2-4) is lshown with a covering of insulation comprising a preformed lower section 36 like that shown in Figure 2 extending along the lower Ap01'- tion of the pipe 24b and welded thereto at 37 and 38 on opposite sides ofthe pipe. A piece of wire fabric 39 is placed around the opposite upper portion of the pipe 24b and is welded to the pipe 24b adjacent the axiallyextending edges of the preformed section 36, preferably with common welds. A layer of plastic refractory material 40 is then imbedded around the Wire fabric 39 against the pipe 24b so that the layer of refractory material provided hy the section 36 around the lower portion of the pipe 24bv is continued around the upper portion thereof. A .fsernicylindrical mold for applying the refractory material-'40 to the upper portion of the pipe 24b is indicated in Figure 8 at 41. In some instances this may be more convenentthan thesystem illustrated in Figures 2-4, since the preformed sections are primarily useful in applying a refractory covering to the lower portion of a horizontal pipe or to any portion of a vertical pipe, where it is difficult to hold unhardened plastic refractory material-inlplace- 4The upper portion of a horizontal-pipe., on thel other hand, cansretain unhardened plastic.refractoryzrnaterial without the necessity of holding-farmold againstwthe lmaterialwhile ity hardens.. It should alsobeobservedinFigure 8l that the wire fabric 3:9fis-oficorwentional.- woventype. Such a woven fabric provides less anchoring structure for the refractory materialxthan ther.interlockingl.coil fabric' illustratedin. Figure :Y6-and described-.in more detail aboveuin connection with.that-digure..l Alsof one setnofy the.cross-strands of woven wire-must .either-be prefor'med'into a semicylind'ricalvr-shape rore1se,.must;.beforcibly bent and held around; thef pipe` during the welding operation. On the other, hand,l,woven fabric. suchcas thatl shown at 39 in FigurefSf contains-less. wire andl is, less expensive than interlocking coiled; wire, and is therefore advantageous where its. lower. vfirst cost `offsets higher maintenance cost. .Figures and 10 illustrate a modified system of forming and securing preformed. insulatingy sections. A pair of@semicylindrical.-preformedinsulating sections 42 and 43 areshown coveringa pipe24c like the pipe 24a, shown 45- beforey thersectionsgare .placed-on the pipe 24e.

in..l"igures,2z4; Thesesections haveV respective .wire bases-4.4:Vv and.. 45eof' wovenL-wire similar to that shown in Eigure, and-.have refractorymaterial.- 46 and 47v cast around and imbedded in' the respective-wire bases 44 and The refractory coverings-Adami 4.7 each extend around thet pipe 24c-so-that their:N adjacent coaxially-extending' edges onfopposite sides ofthe pipe are in closely abutting relationship"f The refractory fmaterial is; omit-ted at spaced intervaIsf-ass'hown-at 48 on oneside of the pipe' and at 49 onthe other-side of the' pipe, t'ofx'pos'e the underlyingwire'bases 44 and 45 so that they-rnay be welded toitlie-pipe -24tvas shown at 50; After the vveldsA 50'` have beenlcompleted' refractory material in plastic form-fisv pasted o very the openings 4S and 49'l along the abutting edges of the sections 42 and 4 3 to complete the refracttnfyl covering.- -;Additional' prftrrrie'd sections are applied tothe pipe 2 4c in the saine ,wayin abutting endto-end relationship toextend the covering as 'required.

lm Figures 1 1 andhlZp adifferent .'systern of attaching a` lwire base; toga supporting pipemis shown, usingv preformed insulating sectlons like those shown in Figure 9 aroundl a similarA pipe. 24d-. -Il is'teadof welding. the wire bases ofthe sectionsgtothe pipe24d;Itrletalstuds 51 are welded to the pipe 24d. before ythe insulating sections are Placed Q11. the.. Pme; andthen the ihsul'atinasections are put in place andthe studsplareubent around, the wire bases :ofthesections to anchor them to the pipe` 24d, as best-shown in Fig'u e 1 2. This system of anchoringthe metal base is applicable to any of the disclosed embodimnts. gf myinventvaandrnakes if Possible to weld anchoring studs ,to supporting'. Pipes; bfrje the Ribes are placed ina-furnace and thenjto fasteninsulation to vthe pipes afterthejpipes are installed inthe furnacewithout thenecessity of bringing. cumbersome welding equipment into thelirnited space inside ,the furnace.

Figures 13515A show a dilerentforni 'of preformed insulatlng section which `is adapted tobe p'refired before being placed xin a furnac e without injury to the wire base, and which h as the further advantage of permitting the I.use of a st eri e s of s eparatewire's fof form'ing the rnetalfanchring structure for the insulating sections so that the amount of vvire in the .base and consequently the cost ofthe yvire baseis reduced'to a mir'rirnum. The illustrated embodiment of vthis -rriodic'ation Ycomprises a pair of full 180 semicylindricl refractory pieces 52 and 53 adapted to fit closely around a metal pipe 24e which is like the pipe 24a in Figures 2-4.A The axially-extending edges of the pieces 52 and 53 are adapted to fit closely together in abutting relationship without any spacing therebetween such as shown in Figure 3 and without any relieved portions such as shown at 48 and 49 in Figure 9. The pieces 52 and 53 are precast separately in suitable molds with a series of axially-extending pieces of straight wire 54 extending therethrough adjacent the inner surfaces thereof. The pieces of wire 54 are left in the molded pieces 52 and 53 if the molded pieces are not to be preiired. However, preiiring improves the strength and durability of the refractory material and the wires 54 are therefore preferably withdrawn after the molded pieces 52 and 53 have hardened sufficiently, and the molded pieces are then prered in a furnace suitable for that purpose.- The use of straight wires makes it possible to remove the wires 54 to protect them from the unrelieved heat in the preiiring furnace, and after prefiring to replace the wires in the pieces 52 and 53, with the ends of the wires protruding from the opposite ends of the molded pieces. The protruding ends of the wires can be separately secured to the pipe 24e to anchor the pieces 52 and 53 thereon but preferably semicircular lengths of wire 55 and 56 are welded to the ends of the wires 54 protruding from the respective opposite ends of the piece 52, and like semicircular lengths of wire 57 and 58 are welded to the corresponding protruding ends of the wires S4 in the piece 53. The resultant prefabricated insulating sections can then be secured to the pipe 24C in a convenient manner by welding the opposite ends of the various wires 55--58 to the pipe 24e, as indicated at 59 in Figure l5. For purposes of illustration the welds 59 at the ends of the wires 55 and S7 are shown separately in Figure l5 but in practice it is preferable to weld the adjacent ends of these wires in a single welding operation, so that only four welds are necessary to anchor two opposite insulating sections of the kind in question to a supporting pipe. Additional insulating sections of the same kind are added in the same way in spaced end-to-end relationship, and the spaces between the adjacent ends are filled with plastic refractory material after the welding operation has been completed, as indicated at 60 in Figure 13. Anchoring studs like those shown at 51 in Figures 11 and 12 may be used instead of the welds 59 to anchor the wires 55-58.

The differences between the various forms of construction described above are of importance principally from the point of View of installation and maintenance. The thermal effects of the different forms of construction in their completed form are generally the same, although the shape and amount of wire in the anchoring base will have some slight effect on thermal conductivity. In all cases the refractory covers its wire base and the underlying metal pipe without any air gap in between, and as the result the rate of thermal adsorption of the pipe is sufficient to lower the temperature of the refractory material to safe limits, even near the outer surface of relatively thick pieces of refractory material, and also to lower the temperature of the wire anchoring base, which is close to the pipe and in occasional metal-to-metal contact with it, to even lower temperature limits safe for heat resistant metal. For example, with a woven wire base similar to that shown in Figure 8 welded to a 1% water-cooled pipe and with a thick layer of refractory material around the pipe, I have found that with a furnace temperature just over 2700 F. the ternperature of the outer surface of the refractory reaches just under 2600 F., the temperature of the refractory below its outer surface reaches less than l700 F., the Wire temperature reaches about 1200 F., and the pipe surface temperature reaches about 250 F., with a pipe surface heat adsorption of about 28,000 B. t. u. per square foot of pipe surface per hour. These figures are illustrative of the fact that insulation in accordance with my invention is highly successful in holding down temperatures in the interior portions of a refractory covering for a pipe in a high temperature furnace, while at the same time holding down the heat loss to the cooling fluid in the pipe.

While I have illustrated and described certain present preferred embodiments of the invention and methods of practicing the same it will be realized that the invention is not limited thereto but may be otherwise variously `6 embodied and practiced within the scope of the following claims.

I claim:

1. In a furnace, an elongated heat absorptive member, an interconnected reticulated metal structure fastened to said member and extending closely around and partly against said member, and refractory material imbedded in and solidly covering the reticulated metal structure and the underlying member with substantially no air space therebetween, whereby the anchoring structure is protected against the furnace heat by its close association with the heat-absorptive member and by the overlying refractory material, and the refractory material is protected from excessive temperature by transfer of its heat through the anchoring structure to the heat-absorptive member.

2. In a furnace for heat-treating metal workpieces, an elongated hollow metal member, means for passing cooling fluid through the hollow interior of said member and extending closely around and partly against said member, a structure of connected wires fastened to said member, and refractory material imbedded in and solidly covering the wires and fitting against the underlying outer surface of the said member with substantially no air space therebetween, whereby the anchoring structure is protected against the furnace heat by its close association with the heat-absorptive member and by the overlying refractory material, and the refractory material is protected from excessive temperature by transfer of its heat through the anchoring structure to the heat-absorptive member.

3. In a furnace for heat-treating metal workpieces, an elongated hollow metal member, means for passing cooling fluid through the hollow interior of said member, a structure of connected wires fastened to said member and extending closely around and partly against said member, metal studs welded to said member and bent around wires of said structure to fasten them to the member, and refractory material imbedded in and solidly covering the interlocking wires and studs and fitting against the underlying outer surface of the said member with substantially no air space therebetween, whereby the anchoring structure is protected against the furnace heat by its close association with the heatabsorptive member and by the overlying refractory material, and the refractory material is protected from excessive temperature by transfer of its heat through the anchoring structure to the heat-absorptive member.

4. In a furnace for heat-treating metal workpieces, an elongated hollow metal member, means for passing cooling iiuid through the hollow interior of said member, a structure of woven wires fastened at intervals to said member and extending closely around and partly against said member, and refractory material imbedded in and solidly covering the wires and the wire fastenings, and fitting against the underlying outer surface of said member with substantially no air space therebetween, whereby the anchoring structure is protected against the furnace heat by its close association with the heatabsorptive member and by the overlying refractory material, and the refractory material is protected from excessive temperature by transfer of its heat through the anchoring structure to the heat-absorptive member.

5. In a furnace for heat-treating metal workpieces, an elongated hollow cylindrical metal member, means for passing cooling fluid through the hollow interior of said member, a structure of interlocking wires fastened at intervals to said member and extending closely around and partly againstsaid member, each wire being formed generally helically with its helical axis disposed parallel to the axis of said member, and refractory material imbedded in and solidly covering the wires and the wire fastenings, and fitting against the underlying outer surface of said member with substantially no air space therebetween, whereby the anchoring structure is protected against the furnace heat by its close association with the heat-absorptive member and by the overlying refractory material, and the refractory material is protected from excessive temperature by transfer of its heat through the anchoring structure to the heat-absorptive member.

6. A method of prefabricating a preiired, reinforced refractory cover for a support in a heat-treating furnace, comprising the steps of casting refractory material with wires imbedded therein, withdrawing the wires, prering the cast refractory material without the wires, and replacing the wires.

7. A method of covering a metal pipe in a heattreating furnace with a preired,- reinforced refractory cover,` comprising the; steps of casting a semicylindrical refractory section with separate straight wires extending axially therethrough adjacent its inner surface, said section being cast while sep'aratedfrom the pipe but adapted to fit closely therearound, withdrawing the wires after hardening ofthe refractory andr preiiring the refractory, replacing the wires with their opposite ends projecting from the prefired piece, fastening asemicircular piece of wire to the adjacent projecting wire ends at each end of the prered piece, placing the refractory in close ttingengagement around the pipe, and fastening each of the semicircular pieces of wire to the pipe. t

v8. In an insulated high temperature f chamber, an elongated membentherein and insulation covering'the member, said insulationl comprising a series of arcuate abutting sections each having a reticulated metal structure `fastened closely around and partly against a portion of the member and having refractory material embedded in' and solidlycoveringfthe reticulated metal structure and Ythe underlying portion of the member with substantially no air space between the Arefractory material and the underlying p'ortionvof the member, said reticulated metal structure furtherl extending over substantially the entire angulars'pan of said arcuate sections and being secured to said member adjacent each longitudinally extending. edge ofl said sections.

`9. In an insulated high temperature chamber, an elongated member therein andinsulation covering the member, said insulation' comprising a series of arcuate abutting sections each having a wire structure extending closely around and partly against a portion of the member. and having refractory material embedded in and solidly covering the wire and the. underlying portion of the elongated member with substantially no air space betweenthe refractory material and the underlying portion of the member, Asaid member having studs secured theretok and bent around portions of the wire of the respective insulation sections adjacent the longitudinally extending edges of said sections to facilitate attaching and detaching the sections, said wire structure further extending over substantially the entire angular span of said arcuate sect-ions.`

10. In a furnacea tubular metal member therein to be thermally insulated, said tubular member being adapted to have a cooling u'id passed therethrough, a preformed insulating section having an arcuate inner surface tting closely against the outside of said member, said section extending around a part of the circumference of said member, said section further comprising a block of refractory and a wire structure embedded in said block proximate to said surface, said block being boundedby edges at the ends and sides thereof, a plurality of portions of said wire structure projecting at least from opposite edges of said block adjacentl said outside of said member, said projecting portions of said wire structure. being substantially directly connected to said memberl to fasten said section to said member.

References Cited in the file of this patent UNITED STATES PATENTS Number v. Name Date 555,693 Geraerdts Mar. 3,- 1896 718,214 OBrien Ian. 13, 1903 1,424,948 Stoop Aug. 8, 1922 1,440,218 French Dec. 26, 1922 r1,506,173 Hagen et al. Aug. 26, 1924 1,624,386y Betts Apr. 12, 1927 1,670,557 Wettstein May 22, 1928 1,753,220 Staribery et al.- Apr'.` 8, 1930 1,969,374 Kleffel Aug. 7, 1934 2,022,649 Corriston Dec. 3, 1935 2,154,619 1939l 2,173,107 1939 2,261,583 Hemphill Nov. 4, 1941 2,435,362 Morton Feb. 3, 1948 2,436,452 Schmidtl Feb. 24, 19.48

2,482,878 Schmidt Sept. 27, 1949 

